Java

Questions and Answers

• How can you achieve runtime polymorphism in Java?
  1. method overloading
  2. method overrunning
  3. method overriding
  4. method calling
• Given the following definitions, which of these expression will **NOT** evaluate to true?
  1. `(i1 | i2) == 3`
  2. `i2 && b1`
  3. `b1 || !b2`
  4. `(i1 ^ i2) < 4`
• What is the output of this code?
  1. It will not compile because of line 4.
  2. It will not compile because of line 3.
  3. 123
  4. 1234
• Which of the following can replace the CODE SNIPPET to make the code below print "Hello World"?
  1. `super1.print(); super2.print();`
  2. `this.print();`
  3. `super.print();`
  4. `Interface1.print(); Interface2.print();`
• What does the following code print?
  1. CD
  2. CDE
  3. D
  4. "abcde"
• What is the result of this code?
  1. It will show a stack trace with a runtime exception.
  2. "java.lang.Exception"
  3. It will run and throw an exception.
  4. It will not compile.
• Which class can compile given these declarations?
  1. A
  2. B
  3. C
  4. D
• What is the output of this code?
  1. The code does not compile.
  2. truefalse
  3. truetrue
  4. falsetrue
• Given the following two classes, what will be the output of the Main class?
  1. Lines 1 and 2 generate compiler errors due to class name conflicts.
  2. "-123"
  3. It will throw an exception on line 5.
  4. "123"
• What is the result of this code?
  1. It will not compile because of line 10.
  2. "Hello!"
  3. It will not compile because of line 2.
  4. "World!"
• Given this code, which command will output "2"?
  1. `java Main 1 2 "3 4" 5`
  2. `java Main 1 "2" "2" 5`
  3. `java Main.class 1 "2" 2 5`
  4. `java Main 1 "2" "3 4" 5`
• What is the output of this code?
  1. "123451234512345"
  2. Nothing - this will not compile.
  3. a negative integer value
  4. "12345100000"
• What is the output of this code?
  1. The code does not compile.
  2. A runtime exception is thrown.
  3. "world!!world"
  4. "world!world!"
• How do you write a foreach loop that will iterate over ArrayList\pencilCase?
  1. `for (Pencil pencil : pencilCase) {}`
  2. `for (pencilCase.next()) {}`
  3. `for (Pencil pencil : pencilCase.iterator()) {}`
  4. `for (pencil in pencilCase) {}`
• What does this code print?
  1. `0`
  2. positive number
  3. negative number
  4. compilation error
• You have an ArrayList of names that you want to sort alphabetically. Which approach would **NOT** work?
  1. `names.sort(Comparator.comparing(String::toString))`
  2. `Collections.sort(names)`
  3. `names.sort(List.DESCENDING)`
  4. `names.stream().sorted((s1, s2) -> s1.compareTo(s2)).collect(Collectors.toList())`
• By implementing encapsulation, you cannot directly access the class's \_ properties unless you are writing code inside the class itself.
  1. private
  2. protected
  3. no-modifier
  4. public
• Which is the most up-to-date way to instantiate the current date?
  1. `new SimpleDateFormat("yyyy-MM-dd").format(new Date())`
  2. `new Date(System.currentTimeMillis())`
  3. `LocalDate.now()`
  4. `Calendar.getInstance().getTime()`
• Fill in the blank to create a piece of code that will tell whether `int0` is divisible by `5`:
  1. `int0 / 5 ? true: false`
  2. `int0 % 5 == 0`
  3. `int0 % 5 != 5`
  4. `Math.isDivisible(int0, 5)`
• How many times will this code print "Hello World!"?
  1. 10 times
  2. 9 times
  3. 5 times
  4. infinite number of times
• The runtime system starts your program by calling which function first?
  1. print
  2. iterative
  3. hello
  4. main
• What code would you use in Constructor A to call Constructor B?
  1. Jedi(name, species, false)
  2. new Jedi(name, species, false)
  3. this(name, species, false)
  4. super(name, species, false)
• Which statement is **NOT** true?
  1. An anonymous class may specify an abstract base class as its base type.
  2. An anonymous class does not require a zero-argument constructor.
  3. An anonymous class may specify an interface as its base type.
  4. An anonymous class may specify both an abstract class and interface as base types.
• What will this program print out to the console when executed?
  1. [5, 1, 10]
  2. [10, 5, 1]
  3. [1, 5, 10]
  4. [10, 1, 5]
• What is the output of this code?
  1. "Hello"
  2. A runtime exception is thrown.
  3. The code does not compile.
  4. "ello"
• Object-oriented programming is a style of programming where you organize your program around \_ rather than \_ and data rather than logic.
  1. functions; actions
  2. objects; actions
  3. actions; functions
  4. actions; objects
• What statement returns true if "nifty" is of type String?
  1. `"nifty".getType().equals("String")`
  2. `"nifty".getType() == String`
  3. `"nifty".getClass().getSimpleName() == "String"`
  4. `"nifty" instanceof String`
• What is the output of this code?
  1. A runtime exception is thrown.
  2. 3false
  3. 2true
  4. 3true
• What is the result of this code?
  1. It will not compile because of line 7.
  2. Hello!Hello!
  3. Hello!World!
  4. It will not compile because of line 11.
• What method can be used to create a new instance of an object?
  1. another instance
  2. field
  3. constructor
  4. private method
• Which is the most reliable expression for testing whether the values of two string variables are the same?
  1. string1 == string2
  2. string1 = string2
  3. string1.matches(string2)
  4. string1.equals(string2)
• Which letters will print when this code is run?
  1. A, B, and D
  2. A, C, and D
  3. C and D
  4. A and D
• What is the output of this code?
  1. It will throw a runtime exception.
  2. It will not compile.
  3. It will print "Hello World!" three times.
  4. It will run forever.
• What is the output of this code?
  1. `[abc, 0, 2, 10]`
  2. The code does not compile.
  3. `[abc, 2, 10, 0]`
  4. `[0, 10, 2, abc]`
• What is the output of this code?
  1. Hello World!
  2. HelloHelloWorld!
  3. Hello Hello World!
  4. Hello HelloWorld!
• What is displayed when this code is compiled and executed?
  1. x
  2. null
  3. 10
  4. 5
• Which approach cannot be used to iterate over a List named _theList_?
  1. A
  2. B
  3. C
  4. D
• What method signature will work with this code?
  1. public void isHealthy(String avocado)
  2. boolean isHealthy(String string)
  3. public isHealthy("avocado")
  4. private String isHealthy(String food)
• Which are valid keywords in a Java module descriptor (module-info.java)?
  1. provides, employs
  2. imports, exports
  3. consumes, supplies
  4. requires, exports
• Which type of variable keeps a constant value once it is assigned?
  1. non-static
  2. static
  3. final
  4. private
• How does the keyword `volatile` affect how a variable is handled?
  1. It will be read by only one thread at a time.
  2. It will be stored on the hard drive.
  3. It will never be cached by the CPU.
  4. It will be preferentially garbage collected.
• What is the result of this code?
  1. an alphanumeric character
  2. a negative number
  3. a positive number
  4. a ClassCastException
• You get a NullPointerException. What is the most likely cause?
  1. A file that needs to be opened cannot be found.
  2. A network connection has been lost in the middle of communications.
  3. Your code has used up all available memory.
  4. The object you are using has not been instantiated.
• How would you fix this code so that it compiles?
  1. Make age static.
  2. Make age global.
  3. Make age public.
  4. Initialize age to a number.
• Add a Duck called "Waddles" to the ArrayList **ducks**.
  1. `Duck waddles = new Duck();`
  2. `Duck duck = new Duck("Waddles");`
  3. `ducks.add(new Duck("Waddles"));`
  4. `ducks.add(new Waddles());`
• If you encounter `UnsupportedClassVersionError` it means the code was `___` on a newer version of Java than the JRE `___` it.
  1. executed; interpreting
  2. executed; compiling
  3. compiled; executing
  4. compiled, translating
• Given this class, how would you make the code compile?
  1. A
  2. B
  3. C
  4. D
• How many times f will be printed?
  1. 4
  2. 3
  3. 5
  4. A Runtime exception will be thrown
• Which statements about `abstract` classes are true?
  1. 1, 2, and 3
  2. only 3
  3. 2 and 3
  4. only 2
• Which keyword lets you call the constructor of a parent class?
  1. parent
  2. super
  3. this
  4. new
• What is the result of this code?
  1. It will throw an ArithmeticException.
  2. It will run and output 0.
  3. It will not compile because of line 3.
  4. It will run and output infinity.
• Normally, to access a static member of a class such as Math.PI, you would need to specify the class "Math". What would be the best way to allow you to use simply "PI" in your code?
  1. Add a static import.
  2. Declare local copies of the constant in your code.
  3. This cannot be done. You must always qualify references to static members with the class form which they came from.
  4. Put the static members in an interface and inherit from that interface.
• Which keyword lets you use an interface?
  1. extends
  2. implements
  3. inherits
  4. import
• Why are ArrayLists better than arrays?
  1. You don't have to decide the size of an ArrayList when you first make it.
  2. You can put more items into an ArrayList than into an array.
  3. ArrayLists can hold more kinds of objects than arrays.
  4. You don't have to decide the type of an ArrayList when you first make it.
• Declare a variable that holds the first four digits of ?
  1. int pi = 3.141;
  2. decimal pi = 3.141;
  3. double pi = 3.141;
  4. float pi = 3.141;
• Use the magic power to cast a spell
  1. `new MagicPower().castSpell("expecto patronum")`
  2. `MagicPower magicPower = new MagicPower();`
  3. `MagicPower.castSpell("expelliarmus");`
  4. `new MagicPower.castSpell();`
• What language construct serves as a blueprint containing an object's properties and functionality?
  1. constructor
  2. instance
  3. class
  4. method
• What does this code print?
  1. 10 10
  2. 5 10
  3. 10 5
  4. 5 5
• What is the result of this code?
  1. Hello World
  2. It will not compile because the second catch statement is unreachable
  3. Hello World!
  4. It will throw runtime exception
• Which is not a java keyword
  1. finally
  2. native
  3. interface
  4. unsigned
• Which operator would you use to find the remainder after division?
  1. `%`
  2. `//`
  3. `/`
  4. `DIV`
• Which choice is a disadvantage of inheritance?
  1. Overridden methods of the parent class cannot be reused.
  2. Responsibilities are not evenly distributed between parent and child classes.
  3. Classes related by inheritance are tightly coupled to each other.
  4. The internal state of the parent class is accessible to its children.
• Declare and initialize an array of 10 ints.
  1. `Array numbers = new Array(10);`
  2. `Array[int] numbers = new Array[int](10);`
  3. `int[] numbers = new int[10];`
  4. `int numbers[] = int[10];`
• Refactor this event handler to a lambda expression:
  1. `groucyButton.addActionListener(ActionListener listener -> System.out.println("Press me one more time..."));`
  2. `groucyButton.addActionListener((event) -> System.out.println("Press me one more time..."));`
  3. `groucyButton.addActionListener(new ActionListener(ActionEvent e) {() -> System.out.println("Press me one more time...");});`
  4. `groucyButton.addActionListener(() -> System.out.println("Press me one more time..."));`
• Which functional interfaces does Java provide to serve as data types for lambda expressions?
  1. Observer, Observable
  2. Collector, Builder
  3. Filter, Map, Reduce
  4. Consumer, Predicate, Supplier
• What is a valid use of the hashCode() method?
  1. encrypting user passwords
  2. deciding if two instances of a class are equal
  3. enabling HashMap to find matches faster
  4. moving objects from a List to a HashMap
• What kind of relationship does "extends" denote?
  1. uses-a
  2. is-a
  3. has-a
  4. was-a
• How do you force an object to be garbage collected?
  1. Set object to null and call Runtime.gc()
  2. Set object to null and call System.gc()
  3. Set object to null and call Runtime.getRuntime().runFinalization()
  4. There is no way to force an object to be garbage collected
• Java programmers commonly use design patterns. Some examples are the **\_**, which helps create instances of a class, the **\_**, which ensures that only one instance of a class can be created; and the **\_**, which allows for a group of algorithms to be interchangeable.
  1. static factory method; singleton; strategy pattern
  2. strategy pattern; static factory method; singleton
  3. creation pattern; singleton; prototype pattern
  4. singleton; strategy pattern; static factory method
• Using Java's Reflection API, you can use \_ to get the name of a class and \_ to retrieve an array of its methods.
  1. this.getClass().getSimpleName(); this.getClass().getDeclaredMethods()
  2. this.getName(); this.getMethods()
  3. Reflection.getName(this); Reflection.getMethods(this)
  4. Reflection.getClass(this).getName(); Reflection.getClass(this).getMethods()
• Which is not a valid lambda expression?
  1. `a -> false;`
  2. `(a) -> false;`
  3. `String a -> false;`
  4. `(String a) -> false;`
• Which access modifier makes variables and methods visible only in the class where they are declared?
  1. public
  2. protected
  3. nonmodifier
  4. private
• What type of variable can be assigned to only once?
  1. private
  2. non-static
  3. final
  4. static
• How would you convert a String to an Int?
  1. `"21".intValue()`
  2. `String.toInt("21")`
  3. `Integer.parseInt("21")`
  4. `String.valueOf("21")`
• What method should be added to the Duck class to print the name Moby?
  1. `public String toString() { return name; } `
  2. `public void println() { System.out.println(name); } `
  3. `String toString() { return this.name; } `
  4. `public void toString() { System.out.println(this.name); } `
• Which operator is used to concatenate Strings in Java
  1. `+`
  2. `&`
  3. `.`
  4. `-`
• How many times does this loop print "exterminate"?
  1. two
  2. four
  3. three
  4. five
• What is the value of myCharacter after line 3 is run?
  1. p
  2. r
  3. e
  4. i
• When should you use a static method?
  1. when your method is related to the object's characteristics
  2. when you want your method to be available independently of class instances
  3. when your method uses an object's instance variable
  4. when your method is dependent on the specific instance that calls it
• What phrase indicates that a function receives a copy of each argument passed to it rather than a reference to the objects themselves?
  1. pass by reference
  2. pass by occurrence
  3. pass by value
  4. API call
• In Java, what is the scope of a method's argument or parameter?
  1. inside the method
  2. both inside and outside the method
  3. neither inside nor outside the method
  4. outside the method
• What is the output of this code?
  1. 5
  2. 8
  3. 1
  4. 3
• Which change will make this code compile successfully?
  1. Change line 2 to `public static final String message`
  2. Change line 6 to `public void print2(){}`
  3. Remove the body of the `print2` method and add a semicolon.
  4. Remove the body of the `print` method.
• What is the output of this code?
  1. falsefalse
  2. truetrue
  3. falsetrue
  4. truefalse
• Which code snippet is valid?
  1. `ArrayList words = new ArrayList(){"Hello", "World"};`
  2. `ArrayList words = Arrays.asList("Hello", "World");`
  3. `ArrayList words = {"Hello", "World"};`
  4. `ArrayList words = new ArrayList<>(Arrays.asList("Hello", "World"));`
• What is the output of this code?
  1. A runtime exception is thrown.
  2. "HelloWorld!"
  3. "hello"
  4. ????
• How would you use the TaxCalculator to determine the amount of tax on $50?
  1. TaxCalculator.calculate(50);
  2. new TaxCalculator.calculate(50);
  3. calculate(50);
  4. new TaxCalculator.calculate($50);
• Which characteristic does not apply to instances of java.util.HashSet=
  1. uses hashcode of objects when inserted
  2. contains unordred elements
  3. contains unique elements
  4. contains sorted elements
• What is the output?
  1. 1 3 2 4
  2. 4 2 3 1
  3. 1 2 3 4
  4. 4 3 2 1
• What will this code print, assuming it is inside the main method of a class?
  1. my
  2. hellomyfriends
  3. hello
  4. friends
• You have an instance of type Map named instruments containing the following key-value pairs: guitar=1200, cello=3000, and drum=2000. If you add the new key-value pair cello=4500 to the Map using the put method, how many elements do you have in the Map when you call instruments.size()?
  1. 2
  2. When calling the put method, Java will throw an exception
  3. 4
  4. 3
• Which class acts as root class for Java Exception hierarchy?
  1. Clonable
  2. Throwable
  3. Object
  4. Serializable
• Which class does not implement the java.util.Collection interface?
  1. java.util.Vector
  2. java.util.ArrayList
  3. java.util.HashSet
  4. java.util.HashMap
• You have a variable of named `employees` of type `List` containing multiple entries. The `Employee` type has a method `getName()` that returns te employee name. Which statement properly extracts a list of employee names?
  1. `employees.collect(employee -> employee.getName());`
  2. `employees.filter(Employee::getName).collect(Collectors.toUnmodifiableList());`
  3. `employees.stream().map(Employee::getName).collect(Collectors.toList());`
  4. `employees.stream().collect((e) -> e.getName());`
• This code does not compile. What needs to be changed so that it does?
  1. Add a constructor that accepts a `String` parameter and assigns it to the field `shortCode`.
  2. Remove the `final` keyword for the field `shortCode`.
  3. All enums need to be defined on a single line of code.
  4. Add a setter method for the field `shortCode`.
• Which language feature ensures that objects implementing the `AutoCloseable` interface are closed when it completes?
  1. try-catch-finally
  2. try-finally-close
  3. try-with-resources
  4. try-catch-close
• What code should go in line 3?
  1. `int[][] array = new int[][];`
  2. `int[][] array = new int[3][3];`
  3. `int[][] array = new int[2][2];`
  4. `int[][] array = [][];`
• Is this an example of method overloading or overriding?
  1. neither
  2. both
  3. overloading
  4. overriding
• Which choice is the best data type for working with money in Java?
  1. float
  2. String
  3. double
  4. BigDecimal
• Which statement about constructors is not ture?
  1. A class can have multiple constructors with a different parameter list.
  2. You can call another constructor with `this` or `super`.
  3. A constructor does not define a return value.
  4. Every class must explicitly define a constructor without parameters.
• What language feature allows types to be parameters on classes, interfaces, and methods in order to reuse the same code for different data types?
  1. Regular Expressions
  2. Reflection
  3. Generics
  4. Concurrency
• What will be printed?
  1. raspberry
  2. strawberry
  3. blueberry
  4. rasp
• What is the value of `forestCount` after this code executes?
  1. 3
  2. 4
  3. 2
  4. When calling the put method, Java will throw an exception
• What is a problem with this code?
  1. String should be compared using == method instead of equals.
  2. Modifying a collection while iterating through it can throw a ConcurrentModificationException.
  3. The List interface does not allow an argument of type String to be passed to the remove method.
  4. ArrayList does not implement the List interface.
• How do you convert this method into a lambda expression?
  1. `Function squareLambda = (int x) -> { x * x };`
  2. `Function squareLambda = () -> { return x * x };`
  3. `Function squareLambda = x -> x * x;`
  4. `Function squareLambda = x -> return x * x;`
• Which choice is a valid implementation of this interface?
  1. A
  2. B
  3. C
  4. D
• What is the result of this program?
  1. 10
  2. 20
  3. null
  4. An error will occur when compiling.
• Which statement must be inserted on line 1 to print the value true?
  1. `Integer val = 15;`
  2. `String val = "Sam";`
  3. `String val = null;`
  4. `Optional val = Optional.empty();`
• What will this code print, assuming it is inside the main method of a class?
  1. false
     true
  2. true
     true
  3. true
     false
  4. false
     false
• What will this code print?
  1. `[Two]`
  2. `[One, Two, Three]`
  3. `[One, Three]`
  4. `Two`
• Which code checks whether the characters in two Strings,named `time` and `money`, are the same?
  1. `if(time <> money){}`
  2. `if(time.equals(money)){}`
  3. `if(time == money){}`
  4. `if(time = money){}`
• An **\_** is a serious issue thrown by the JVM that the JVM is unlikely to recover from. An **
  1. exception,assertion
  2. AbnormalException, AccidentalException
  3. error, exception
  4. exception, error
• Which keyword would not be allowed here?
  1. static
  2. protected
  3. public
  4. void
• Which OOP concept is this code an example of?
  1. composition
  2. generics
  3. polymorphism
  4. encapsulation
• What does this code print?
  1. true; false
  2. false; false
  3. false; true
  4. true; true
• What keyword is added to a method declaration to ensure that two threads do not simultaneously execute it on the same object instance?
  1. native
  2. volatile
  3. synchronized
  4. lock
• Which is a valid type for this lambda function?
  1. `Function`
  2. `Function`
  3. `Function`
  4. `Function`
• What is displayed when this code is compiled and executed?
  1. 6
  2. 3
  3. 4
  4. 7
• What variable type should be declared for capitalize?
  1. `Function`
  2. `Stream`
  3. `String`
  4. `Map`
• Which is the correct return type for the processFunction method?
  1. `Integer`
  2. `String`
  3. `Consumer`
  4. `Function`
• What function could you use to replace slashes for dashes in a list of dates?
  1. `UnaryOperator replaceSlashes = date -> date.replace("/", "-");`
  2. `Function replaceSlashes = dates -> dates.replace("-", "/");`
  3. `Map replaceSlashes = dates.replace("/", "-");`
  4. `Consumer replaceSlashes = date -> date.replace("/", "-");`
• From which class do all other classes implicitly extend?
  1. `Object`
  2. `Main`
  3. `Java`
  4. `Class`
• How do you create and run a Thread for this class?
  1. `Thread thread = new Thread(new CurrentDateRunnable()); thread.start();`
  2. `new Thread(new CurrentDateRunnable()).join();`
  3. `new CurrentDateRunnable().run();`
  4. `new CurrentDateRunnable().start();`
• Which expression is a functional equivalent?
  1. A
  2. B
  3. C
  4. D